"Safety Not Guaranteed" is a film with four concurrent storylines: an investigation into the activities of a man who claims to be able to travel through time, the rekindling of a love affair between two people who dated in high school, a nerdy Indian kid's sexual awakening, and the budding romance between a magazine intern and a self-proclaimed time traveler. The film's shot with the shaky-cam, faux-documentary kind of cinematography of a show like "Parks & Recreation" (though none of the characters break the fourth wall and ever talk directly to the camera). The audience is made to believe the time traveler is crazy until it's revealed at the end that his machine really does work and he was telling the truth the whole time.

The film opens with narration from Darius Britt (Aubrey Plaza from Parks & Recreation) who recounts a lifetime of feeling like the oddball in whatever group she was in: she didn't fit in in college, she was the one standing in the corner at parties in high school, and she was the weird kid in most of grade school. Going back far enough in her memories, she pictures herself playing with a turtle outside when her mom was still alive and she was happy. Later in the movie she explains that her mother was killed one night at a gas station because Darius asked her to stop and get chocolate milk after work -- and her mom called her to let her know she got the milk and was on her way home and shortly after that a man grabbed her and murdered her. Darius has been morose and has blamed herself for her mother's murder ever since.

Darius is now an intern at Seattle Magazine where Bridgit is the editor (played by Mary Lynn Raajskub in a cameo). Bridgit is caustic and berates the interns (while also sleeping with the reporters, though not simultaneously). At a story meeting where Bridgit screams at the staff for new ideas Jeff (played by Jake M. Johnson) suggests doing a story on an ad he saw in the newspaper from a man who claims he can time travel. The ad read: WANTED: Someone to go back in time with me. This is not a joke. You'll get paid after we get back. Must bring your own weapons. Safety not guaranteed. I have only done this once before. NOTE: That last sentence is very important later, because the man in the ad really is a time-traveler and the movie ends up being a documentation of his SECOND trip back through time.

Jeff suggests an article where they track down the person who posted the ad to see if it's a big joke or if the person has mental problems; Bridgit approves the story and assigns Darius and Arnau (the nerdy Indian kid, played by Karan Soni) to work as interns for Jeff. The three immediately proceed to a small town by the seaside where the ad's post office box is located -- which also just so happens to be the town where Jeff grew up. It seems he found the ad because he was occasionally looking in his hometown's paper while keeping tabs on Liz (Jenica Bergere), a hot girl from high school whom Jeff had a wild sexual fling with when they were both students but whom he hasn't seen or talked with in years. In the interim, Liz gained a lot of weight, got married to a pro baseball player, divorced that guy, and then settled into life as a homemaker who raises chickens, bakes pies, and is content being a hairdresser at a local salon and a woman comfortable with her weight and quiet lifestyle (essentially the opposite of the wild, hot girl that Jeff remembers from the old days).

While Jeff sets about finding and reconnecting with Liz, he assigns Darius and Arnau to discern the identity of the time traveler. This is achieved easily by staking out the post office in town and spying through a window to see who picks up the mail for the post office box identified in the ad. Darius soon spots Kenneth (Mark Duplass) pick up the mail and head into his little yellow car; she follows him, leaving Arnau on the sidewalk because he was too timid to follow someone in a car. Kenneth goes to work -- which is in a grocery store -- and Darius asks a coworker for Kenneth's name under the guise of pretending to want to leave a positive comment card for him. It's established that Kenneth is seen as a weirdo by his coworkers and spends most of his time going on about quantum mechanics; his only friend seems to be an elderly black man named Shannon whose wife is ill (later in the film, right before he leaves on his time travel mission, Kenneth will give every cent he has to Shannon in a shoe box so he can help his wife get better).

Darius meets up with Jeff and Arnau at a bar and tells them Kenneth's name and where he works. Arnau has helped Jeff locate Liz on Facebook, though she does not have a picture posted. Jeff sends Liz a message and they agree to meetup at her hair salon and catch up. Jeff also starts the process of trying to get Arnau out of his shell and loosen up so that he can lose his virginity on this road trip. Jeff, being shallow, eventually chickens out of talking to Liz at first because when he finally sees her at her salon she is much heavier than he remembered and he misses the girl in his memory. It will take a while for him to go to Liz's house to meetup with her.

Jeff uses his connections at the paper to find Kenneth's home address, which is a dilapidated old house in the woods. Jeff approaches Kenneth and pretends to be someone interesting in the ad and becoming a time traveling companion but Kenneth sees through him immediately and tells him to leave, thinking that he's just there to make fun of him. Darius is then sent to interact with Kenneth at the grocery store because Jeff figures that Kenneth will like her better. If you've seen the actress Aubrey Plaza on Parks & Recreation, she plays a slightly toned down version of her character on that show in this movie...she has a dry comedic style and flirts by making "big eyes" at Kenneth in between snarky quips. This works well on him and Darius leaves her phone number on a soup can for him to call her.

Kenneth calls and it's decided they should meet in a secret location to talk about "the mission" -- but Kenneth is paranoid that government agents are after him and he needs to make sure that Darius is not "one of them". Jeff and Arnau are in the car with Darius, ducking down so that Kenneth doesn't see them. Suddenly another car pulls up behind Darius -- totally random people who are not involved in things -- and Kenneth gets spooked thinking they are being followed. Kenneth aborts the meeting and says he will call Darius to setup another meeting.

Darius already clearly has feelings for Kenneth at this point and is excited by this adventure.

The next time Darius and Kenneth meet it's in a restaurant to talk about the mission and going back in time -- but Kenneth is cagey about what he wants to do and why. At breakfast Darius notices there is something wrong with Kenneth's ear and he reveals it's a prosthetic because he was born with a defect and his parents could only afford to fix one ear. Kenneth has a freakout and races out to his car, attempting to leave, but Darius stops and reassures him and he trusts her to go further in the training for the mission than anyone else has ever gone before.

Kenneth and Darius then bond over running through the woods, shooting guns at bottles, and pretending to evade government agents who want to stop Kenneth from traveling through time.

Kenneth takes Darius to a white van he's acquired and they drive to a medical research company where Kenneth claims something he needs is being kept. Kenneth, dressed up in all black like a cat burglar, gets the drop on a security guard and locks him in a cage in the garage while Darius waits in the van as the driver. Kenneth sneaks into a storage room -- that just happens to be across the hall from an office party of some kind that's going on. Literally, everyone who works at the company seems to be gathered there, but they are too focused on eating cake and talking to notice Kenneth stealing from them. In the storage room, Kenneth loads up a cart with a half dozen large boxes containing prototypes for advanced lasers. He's not even discovered by the two office workers making out in the storage room. But, when Kenneth opens the door to take the boxes into the hallway everyone in the party sees him but has no idea what he's doing -- and they just stare at him as he steals the lasers. Kenneth is allowed to leave the building with what he's stolen, even though a handful of the workers sheepishly call out "Hey, who are you and what are you doing?". Darius drives the van away after Kenneth loads it up with the lasers and the two of them drive the van to Kenneth's car before abandoning the van and taking off in the car to throw anyone off their trail.

Kenneth now feels like he can trust Darius and has no idea she is an intern at a magazine doing a story on him. In the woods by a campfire, Kenneth reveals he wants to go back to 2001 to save his former girlfriend Belinda from being killed by a car crashing through the front of her house. This is when Darius says she'd go back in time to save her mother from being killed by that man at the gas station. She also tells Kenneth that she regrets not even being nice to her mom when she asked for the chocolate milk that ended up getting her killed. Kenneth plays a romantic song on a zither (Persian guitar) and the two of them kiss for the first time.

The next day, in the woods Kenneth shows Darius the time traveling failsafe warning device: it's a little metal box that has been inside an old rusted truck in the woods for many years; it was there in 2001, so if they travel back to that year and there's any kind of problem, then they must leave a note in this box so that their future selves will find it and know not to go back in time. Kenneth opens the box and it's empty -- which in his logic means that there was no problem encountered in the time traveling and the mission is going to be a success. Kenneth tells Darius that when he was a kid he used to hid his Star Wars figures in the box so that the other boys who picked on him would not find them and throw them into the fire.

Jeff ends up having lots of sex with Liz and realizes that though she's not the hot young girl he fooled around with in high school, he loves being with her and asks her to move back to Seattle with him -- but Liz says no and Jeff gets angry and storms back to Arnau and decides to get the Indian nerd drunk that night. They go to a dive bar, then to some kind of amusement park with bumber cars and go carts, and end up picking up two girls and their gay, Goth friend whom Jeff nicknames "Halloween". After a lot of drinks and some coaching from Jeff, Arnau finally has sex with one of the girls while Jeff smokes cigarettes with Halloween outside. The next morning, Bridgit calls Jeff to tell him that she tracked down the girlfriend that Kenneth said died in that car crash -- but she's alive.

Darius then goes to meet with this girl, named Belinda (played by Kristen Bell from Veronica Mars), who explains that Kenneth was always odd and had a crush on her but she did not reciprocate or encourage him. She tells Darius that Kenneth actually crashed his car through her boyfriend's house but that no one was injured -- and that she has not seen Kenneth since then but wishes him well.

The audience is left to believe that Kenneth is crazy at this point...but what really happened is that on his first trip back through time, Kenneth did something to save Belinda's life that changed reality as we know it. Since she would have been killed in 2001 by a car crashing into her house, Kenneth changed that fate by crashing a car into her boyfriend's house before Belinda and Kenneth ever dated in that time stream. This was the "I've only done this once before" part of the time traveling ad Kenneth posted. Belinda is alive, but has no memory of dating Kenneth because that never happened in this new reality. Belinda is alive and well but is now married to someone else while Kenneth works in a grocery store trying to put together a new time machine so he can go back to fix things in 2001 again so this time he gets to be with Belinda...and apparently he's realized he needs another person to go back with him in order to make things work out the way he wants them to.

Darius doesn't understand all this but she loves Kenneth and wants to get him help; she races to his house but he's not there and instead she discovers the place is full of all sorts of charts, graphs, and scientific schematics. Jeff and Arnau come too, and they all discover that government agents really are following Kenneth. A slow motion chase ensues where the agents follow Kenneth in his car while the trio of reporters follow the agents until Kenneth realizes he's being followed. The agents end up pulling the trio over and telling them that Kenneth is suspecting of breaking into two separate research facilities and stealing equipment -- as well as corresponding with scientists all over the world about time travel. This put him on a government watch list, though the agents never say what agency they are with.

A short time later, after Kenneth loses everyone, Darius meets him back at his house where they have a fight and she tells him he's crazy. He tells her that he's going to launch the mission that day at 5pm and that he no longer wants her to come with him.

It's then a chase to the "mission site", which is on a lake in the middle of the woods. Darius, Jeff, Arnau, and the government agents arrive just in time to see Kenneth climb aboard a swamp boat with a giant fan on the back (like the kind you see zooming through the Everglades in movies). The boat has a weird spinning device in the center and is fitting with Tesla coils that are sparking electricity. There's a hum building as Kenneth prepares to hit the ignition.

Darius runs up to him and tells Kenneth she's sorry and he forgives her. She gets on the boat and Kenneth tells her that they are going back in time, but this time he's "going back for her". He tells Darius to flip the switch and a beam of light launches into the sky (must have been the lasers he stole). Then, a temporal bubble appears and swallows the boat and in a WHOOSH! they disappear.

Jeff, Arnau, and the agents stand there dumbfounded -- the way the grown-ups in 80s movies like ET or The Goonies stood there and stared in jaw-dropped awe at the weird things they witnessed at the end of those movies.

It is not outright stated, but is implied, that Kenneth and Darius went back in time to save her mom and that Kenneth has now let go of trying to change time and be with Belinda again because he is now with Darius.